1. Field of the Invention
Manually actuated magnetic fields in permanent magnet chucks, holders, and lifting devices have been used for decades on ferromagnetic materials (targets). Common applications are seen on mills, grinders, lathes, drills, and other industrial and commercial equipment. Other applications include fixtures, tool and gauge holders, material alignment, and holding fixtures. Various permanent magnet-based lifters are used for material handling and robotic pick-and-place equipment. Unfortunately, the majority of these switchable permanent magnets have relatively low magnetic performance-to-weight ratios. Consequently, magnetic chucks, holders, and lifting devices are often costly or heavy and bulky in order to meet performance objectives.
Permanent magnets produce their own persistent magnetic fields. Permanent magnets have both a north (“N”) and a south (“S”) pole. By definition, the direction of the local magnetic field is the direction that the north pole of a compass (or of any magnet) tends to point. Magnetic field lines exit a magnet near its north pole and enter near its south pole but inside the magnet, the field lines return from the south pole back to the north pole. The “magnetic pole separation line” is used to depict a theoretical plane between the north and south poles of the permanent magnet. Permanent magnets are made of ferromagnetic materials such as iron and nickel that have been magnetized. The strength of a magnet is represented by its magnetic moment (“M”). For simple magnets, M points in the direction of a line drawn from the south to the north pole of the magnet. “Like” magnetic poles, for example, N and N or S and S, when brought near each other repel, while “opposite” magnetic poles, for example, N and S, attract.
All permanent magnets and materials that are strongly attracted to them are ferromagnetic. When the magnetic moment of atoms within a given material can be made to favor one direction, they are said to be “magnetizable.” Ferromagnetism is the basic mechanism by which certain materials form or exhibit strong interactions with magnets.
A material that is magnetically soft is similar to permanent magnets in that it exhibits a magnetic field of its own when in the influence of an external magnetic field. However, the material does not continue to exhibit a magnetic field once the applied field is reduced to zero. Such materials act as a “conduit” carrying, concentrating, and shaping magnetic fields. Proper matching (as described in the Detailed Description of the Invention) of this “conduit” to a specific magnet or group of magnets aligned with common pole orientation, that is, all north poles on one side and all south poles on the opposite side, define a “pole conduit”.
Affixing a properly matched pole conduit to each side of a permanent magnet's or magnets' magnetic poles defines a basic core element. Pole conduits contain and redirect a permanent magnet's magnetic field to the upper and lower faces of the pole conduits. Each pole conduit affixed to the permanent magnet now contains the magnetic field and pole direction of the permanent magnet so that one pole conduit of the core element contains the permanent magnet's north field and the other pole conduit contains the permanent magnet's south field.
By containing and redirecting the magnetic field within the pole conduits, like poles have a simultaneous level of attraction and repulsion. Relative positioning of two or more core elements is critical for proper operation of the apparatus. Aligning upper core element pole conduits with lower core element pole conduits “in-phase”, that is, north-north/south-south (N-N/S-S), activates the apparatus by redirecting the combined magnetic fields of the adjacent pole conduits into a target. Upper and lower core elements anti-aligned or “out-of-phase,” that is, north-south/south-north (N-S/S-N), results in the adjacent pole conduits containing opposing fields and deactivation of the apparatus.
A core element must function as a single entity and may require containment of its separate components into a “carrier platter” in order to facilitate the relative positioning of two or more core elements with respect to each other. The carrier platter further allows for incorporation of two or more core elements into other devices as described further in the Detailed Description of the Invention.
Ferromagnetic materials like iron that show saturation are composed of magnetic domains in microscopic regions that act like tiny permanent magnets. Before an external magnetic field is applied to the material, the magnetic domains are oriented in random directions and thus cancel each other out. When an external magnetizing field “H” is applied to the material, it penetrates the material and aligns the domains, causing their tiny magnetic fields to turn and align parallel to the external field, adding together to create a large magnetic field which extends out from the material. This is called “magnetization”: the stronger the external magnetic field, the more the domains align. Saturation occurs when practically all of the magnetic domains are aligned, so further increases in the applied field cannot cause further alignment of the magnetic domains.
Target saturation is very similar to magnetic saturation in that once all of the magnetic domains in the target material directly under the pole conduit or magnet are saturated, any excess magnetic field cannot be absorbed. If a switchable permanent magnet produces a field in excess of what a target can absorb, the excess magnetic field will result in increased actuation force. Actuation force is the force required to overcome the magnetic resistance between two or more adjacent core elements when orienting one core element with respect to the adjacent core element so as to be aligned in-phase (N-N/S-S). This excess magnetic field must be overcome when rotating adjacent magnetic carrier platters in-phase. Actuation force to align core element pairs can be ten times greater in air or on a very thin target than when on a target that does not fully saturate (absorb the entire magnetic field).
Breakaway force is the force required to separate a magnet perpendicularly from a target. Most magnets are tested on a target with sufficient thickness to avoid oversaturation in the area directly under the pole or poles. Since the breakaway strength is primarily a function of the pole area and the saturation of the material, it is the material and not the magnetic field that determines the breakaway force once a target thickness has become saturated. A magnet that has a breakaway force of 100 Newtons on material 25 mm in thickness may also be at 100 Newtons on material 12 mm in thickness but drop to 70 Newtons on material 6 mm in thickness and 10 Newtons on material 2 mm in thickness.
Magnetic permeability (dimensionless as it is relative to magnetic permeability of a vacuum or air) can often be considered as magnetic conductivity. There are essentially four categories of magnetically permeable substances: (1) Substances whose magnetic permeability is less than one are said to be diamagnetic. These substances to a very small extent produce an opposing magnetic field in response to a strong magnetic field. Because this response is often extremely weak, most non-physicists would consider diamagnetic substances to be nonmagnetic; (2) Substances whose magnetic permeability is exactly one are said to be nonmagnetic. Air or a vacuum has a magnetic permeability of one; (3) Substances with a magnetic permeability greater than one are said to be paramagnetic; and (4) Substances with a magnetic permeability much greater than one (100 to 100,000) are said to be ferromagnetic. This invention primarily deals with targets that are ferromagnetic.
FIGS. 4A and 4B refer to a combination of magnets 104a, 104b, 105a, 106a, 106b, 107a and 107b with matched pole conduits 102a and 102b affixed to the permanent magnets' magnetic pole faces, and are defined to be a core element 101. Pole Conduit 102a is affixed and adjacent to the north poles of permanent magnets 104a, 104b, 105a, 105b, 106a, 106b, 107a and 107 and pole conduit 102b is affixed and adjacent to the south poles of permanent magnets 104a, 104b, 105a, 105b, 106a, 106b, 107a and 107. Pole conduit 102a is now considered to be a north pole conduit while pole conduit 102b would be considered a south pole conduit. Pole conduit 102a and 102b are now able to redirect the magnetic field within them to a perpendicular surface 108a and 108b respectively. The perpendicular surfaces 108a and 108b are used to conduct and redirect the magnetic fields within the pole conduits to either an adjacent core element or to a ferromagnetic target.
Phase alignment occurs when pole conduits of two or more core elements are aligned and effectively adjacent to each other. For example, referring to FIG. 15A, core elements 101b and 101a are said to be out-of-phase or anti-aligned when north pole conduit 102c is directly above south pole conduit 102b and south pole conduit 102d is directly above north pole conduit 102a. Conversely, referring to FIG. 15B, core elements are said to be in-phase when north pole conduit 102c is directly above north pole conduit 102a and south pole conduit 102d is directly above south pole conduit 102b. In-phase alignment of core elements results in a repulsive force between the pole conduits (magnetic repulsion) in addition to a moderately strong external magnetic field. Out-of-phase alignment of core elements results in a strong attractive force (magnetic coupling) between the pole conduits along with very little external magnetic field.
Aligning or placing core element 101b in-phase with another core element 101a, as illustrated in FIG. 15B, activates (or actuates) a very strong external magnetic field, provided by an in-phase “magnetic coupling” between the pole conduits that have a simultaneous attractive and repulsive force. Core elements 101a and 101b that are anti-aligned or placed out-of-phase also provide a “magnetic coupling” as illustrated in FIG. 15A. This out-of-phase “magnetic coupling” provides a very strong attractive force between the adjacent pole conduits with little or no external magnetic field; that is, the external magnetic field is deactivated or de-actuated. In-phase core elements in contact with an unsaturated ferromagnetic target have a mildly attractive force between the core elements.
Magnetic field lines provide a simple way to depict or draw the magnetic field. The magnetic field can be estimated at any point using the direction and density of the magnetic field lines nearby. Typically the stronger the magnetic field, then the higher the density of the magnetic field lines.
The magnetic field lines depicted in FIG. 21 provide a visible two dimensional representation of a typical magnetic field. The “visible” field line depicted is not precisely the same as that of an isolated magnet. The introduction of metal filings alters the magnetic field by acting as a pole conduit and redirecting the field. While the filings are shown in a two-dimensional perspective, a three-dimensional field would look similar to an hour glass.
2. Prior Art
U.S. Pat. No. 4,329,673 issued to Uchikune (1982) describes a switching permanent magnet configuration that uses short circuiting of the north and south poles of a diametrically polarized circular magnet into two steel pole plates to deactivate the magnetic circuit (commonly referred to as shunting).
U.S. Pat. No. 4,329,673 issued to Uchikune (1982), is designed so that the apparatus activates when a diametrically polarized circular magnet is rotated 90°, so that the north and south poles of the permanent magnet are aligned perpendicular to the two isolated magnetically soft pole plates, such that one pole plate is magnetized north and the other pole plate is magnetized south. These pole plates are typically separated with a nonferrous material to avoid short circuiting of the field. To deactivate the apparatus, the diametrically polarized magnet is rotated back 90° from the activated state so that the magnetic pole separation line is now aligned perpendicular with each of the magnetically soft pole plates. By aligning the magnetic pole separation line into each of the pole plates, both the north and south pole magnetic fields of the diametrically polarized permanent magnet are directed into each side of the magnetically soft pole plates and are effectively short-circuited. This basic design is relatively inefficient due to the fact that the pole plates must be of sufficient mass to adequately short-circuit the north and south pole magnetic fields without becoming oversaturated. Pole plate mass is determined by using the minimal mass required to eliminate any residual magnetic field emanating from the magnetic poles When the unit is deactivated. When activated, a substantial portion of the magnetic field is absorbed into the large steel plates substantially reducing the performance-to-weight ratio.
U.S. Pat. No. 7,012,495 B2 issued to Kocijan (2006) FIG. 1 Prior Art, describes a diametrically polarized (magnetized) magnet 21, which has a north pole region 23 separated by a diameter 24 (magnetic pole separation line) of the cylindrical surface through the height of the magnet from the south pole region.
U.S. Pat. No. 7,012,495 B2 issued to Kocijan (2006) (FIG. 2—Prior Art) identifies a switchable magnet configuration comprised of a housing 32 and 33 that contains a first permanent magnet 30, a second permanent magnet 31 an actuation means (34, 35, 36, 37, 38, 39, 40, 41, 42, 43 and 44) to cause relative rotation between the first and second magnets. The magnets 30, 31 are diametrically polarized as shown in FIG. 1—Prior Art. The relative rotation between the upper magnet 31 and the lower magnet 30 allows for a more effective means of cancelling the magnetic field when the magnets are oriented north-south. The field cancellation allows the use of a smaller mass of steel for each pole 32 and 33 than the Uchikune design referenced earlier (U.S. Pat. No. 4,329,673). By reducing the steel pole size, more of the magnetic field is available to attract the target, thereby improving the magnet performance-to-weight ratio.
The functional design described by U.S. Pat. No. 7,012,495 B2 issued to Kocijan (2006) is commercially available and depicted by FIG. 3A Prior Art and FIG. 3B Prior Art. Magnet 58 is affixed to the single piece housing 55 (press fit and/or bonded) with diametrically polarized field line 54 perpendicular to the thin wall of the housing 56. A low friction disc 53 is inserted into housing 55 in between the lower magnet 58 and the upper rotatable magnet 52. Rotation of the upper magnet 52 is accomplished through the use of drilled holes 50 and 51 to accommodate a mechanical linkage 60. In order to rotate upper magnet 52 with respect to the lower magnet 58, a clearance 61 is required between the housing 55 and the upper magnet 52. The clearance can be accomplished by machining a larger diameter into housing 55 or by using a smaller diameter upper magnet 52 than lower magnet 58. The magnetic field of the two magnets 52 and 58 is directed into magnet poles (pole conduits) 57 and 59.
The switchable permanent magnetic device described in U.S. Pat. No. 7,012,495 B2 issued to Kocijan (2006) is considerably more efficient than the switchable permanent magnet holding device described in U.S. Pat. No. 4,329,673 issued to Uchikune (1982). That said, the design described by U.S. Pat. No. 7,012,495 B2 issued to Kocijan (2006) requires tight manufacturing tolerances and is relatively expensive to produce. Manufacture of the single piece housing 55 is both material and labor intensive. Machining of a single piece housing 55 (FIG. 3B Prior Art) requires the use of relatively thick solid material (over twice the thickness of either magnet) that is primarily machined away. The clearance 61 (FIG. 3B Prior Art) must have a very smooth finish to avoid scraping off the magnet's plating and it must always accommodate the tolerances of the upper magnet 52 (FIG. 3B Prior Art). Additionally, clearance 61 (FIG. 3B Prior Art) is a substantial air gap that diminishes the magnetic field transfer into the magnet pole pieces 57 and 59 and often must be overcome by use of a stronger, more expensive composition upper magnet 52 than lower magnet 58. Rotation of the upper magnet 52 also requires that a locating feature 50 and 51 be machined into the upper magnet. These features not only weaken the upper magnet's integrity (exposing it to possible breakage), but also negatively affects the quality of the magnetic field. Permanent magnets are made of exceptionally hard brittle materials that oxidize rapidly in air. This is particularly true of neodymium magnets (NdFeB—neodymium iron boron). By having to attach a rotational feature 60 to the upper magnet, the magnet manufacturer must produce custom magnets that have holes 50 and 51 (FIG. 3A Prior Art) or other locating features machined 34 and 35, as seen in FIG. 2 Prior Art, into the magnet blanks before magnetizing and plating. This often requires long lead times, costly tools, large volume purchases, and high prototype expenses. Moreover, locating these features accurately along the magnetic pole separation line 24 (FIG. 1 Prior Art) is difficult and if off more than a few degrees, can result in nonfunctional or compromised performance of the switchable permanent magnet devices. Diametrically polarized magnets also have inherently reduced magnetic efficiencies as the size increases.
A further drawback to U.S. Pat. No. 7,012,495 B2 issued to Kocijan (2006) is the need for top actuation. By having the upper magnet 31 (FIG. 2 Prior Art) inset into the housing 32 and 33, actuation must take place above a lid 43 (FIG. 2 Prior Art). It is often desirable to affix a device to the top surface of the switchable magnet apparatus. Attachment to the device described in U.S. Pat. No. 7,012,495 B2 issue to Kocijan (2006) is often done to one of the vertical sides (resulting in off-center loading) or to a larger yoke style mount that is affixed to opposite vertical surfaces of the poles 32 and 33 (FIG. 2 Prior Art), yet still provides sufficient room to activate or deactivate the device by rotating a knob or lever 180°.
The Switchable Core Element-Based Permanent Magnet Apparatus has several advantages when compared with the prior art:                Ease of actuation: Actuation can be performed by rotational movement of the entire exterior of the upper carrier platter including the top and the sides, allowing far more flexibility for integration into products and fixtures and for easier attachment of peripherals to the apparatus;        Reduced magnet cost: The highly flexible architecture of the invention allows for immediate adaptation of off-the-shelf magnets. As an added benefit, the use of multiple smaller magnets in the core elements can result in a greater magnetic force than a larger single magnet. For specialized applications where a custom magnet is used, it is unnecessary to machine in any special locating features 34 and 35 (FIG. 2 Prior Art) or attachment features into the magnets. Prototyping is now reduced to days instead of months;        Reduced manufacturing tolerances: Simpler magnet shapes that do not require complex machining and field orientation substantially reduce the risk of product failure;        Stronger, more robust design: Elimination of features machined into the magnet substantially increases the magnet's structural strength. Encapsulation of a magnet into a ferrous or nonferrous carrier platter dramatically reduces the risk of magnet damage due to impact or tensional stress forces from the mechanical linkage 60 (FIG. 3a Prior Art) or as described by mechanical linkage 36, 37 and 38 (FIG. 2 Prior Art);        More efficient magnet use: Elimination of the air gap 61 (FIG. 3B Prior Art) required to orient the magnetic poles, allows the use of a lower cost magnet composition. Air gap 613 between stacked pole conduits 301a and 301b as depicted in FIG. 16B, can be made much tighter than air gap 61 between magnet 52 and housing 55 (FIG. 3B Prior Art). The Prior Art design referenced in FIG. 3A must account for machining tolerances of mild steel that is bored into a material with a variable wall thickness (prone to flexure during machining), diameter and concentric variations of custom run magnet material (length cuts are more accurate), off center hole locations 50 and 51 (centers the magnet within the housing), variations in the mechanical linkage 60, variations in the housing 55 due to plating, and variations in the magnets 52 and 58 due to plating and tolerance variation in the lid; and        Lower cost materials—By using a pole conduit that only needs to be slightly thicker than the magnet(s) and approximately the same thickness as the carrier platter, material costs are dramatically reduced. As an example, if U.S. Pat. No. 7,012,495 B2 issue to Kocijan (2006) used two 25 mm thick magnets it would necessitate the purchase of plate steel that is over 52 mm thick (60 mm stock thickness) or to start with large diameter solid rod that is rough cut, machined on a lathe and then machined on a mill. By using separate carrier platters, 25 mm thick plate may be plasma rough cut and final bored on a low cost machining center or extruded and cut to length with very little post machining.        